Gas combustor

ABSTRACT

A gas includes a main pipe, a bypass pipe, a gas sensor and a cooler. The main pipe, as an exhaust pipe, discharges exhaust gas generated at combustion of gas fuel. The bypass pipe branches from the main pipe and is set to be smaller in flow rate of the exhaust gas than the main pipe. The gas sensor is arranged in the bypass pipe to detect a gas contained in the exhaust gas. The cooler cools the bypass pipe.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2021-048685 filed on Mar. 23, 2021.

TECHNICAL FIELD

The present disclosure relates to a gas combustor including an exhaust pipe that discharges exhaust gas at combustion of gas fuel.

BACKGROUND

Gas emission regulations, such as, NOx, CO2, and CO emission regulations, for gas combustors such as water heaters and boilers are becoming stricter year by year. In order to satisfy the gas emission regulations under various conditions, a concentration of specific gas contained in the exhaust gas may be measured and combustion control may be performed according to the measurement result.

SUMMARY

A gas combustor includes a main pipe, a bypass pipe, a gas sensor and a cooler. The main pipe as an exhaust pipe discharges exhaust gas generated at combustion of gas fuel, and the bypass pipe branches from the main pipe and is set to be smaller in flow rate of the exhaust gas than the main pipe. The gas sensor is arranged in the bypass pipe to detect a gas contained in the exhaust gas, and the cooler cools the bypass pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

FIG. 1 is a diagram showing a configuration of a gas water heater according to a first embodiment.

FIG. 2 is an enlarged diagram showing an exhaust pipe portion of FIG. 1.

FIG. 3 is a diagram corresponding to FIG. 2 when the gas water heater is in a low thermal power mode.

FIG. 4 is a diagram corresponding to FIG. 2 when the gas water heater is in a high thermal power mode.

FIG. 5 is a timing chart showing changes in each part when the operation of the gas water heater is started from a stopped state.

FIG. 6 is a diagram illustrating a method for adjusting losses caused by a check valve.

FIG. 7 is a diagram showing a configuration of a gas water heater according to a second embodiment.

FIG. 8 is an enlarged diagram showing an exhaust pipe portion of FIG. 7.

DETAILED DESCRIPTION

Examples of a sensor for detecting a gas contained in exhaust gas are a zirconia sensor and a constant potential electrolysis sensor. However, the zirconia sensor has poor accuracy because it is affected by gas components other than the measurement target gas. The constant potential electrolysis sensor has a relatively good accuracy, but cannot be used in a high temperature environment because it uses an electrolytic solution.

According to a gas combustor of an aspect of the present disclosure, a bypass pipe branches from a main pipe of an exhaust pipe, and a flow rate of exhaust gas is set to be smaller in the bypass pipe than in the main pipe. A gas sensor is placed in the bypass pipe to detect a gas contained in the exhaust gas, and the bypass pipe is cooled by a cooler. According to this configuration, the cooler can be small and low cost because the cooler is just required to cool the bypass pipe having a relatively small flow rate of exhaust gas. Therefore, it is possible to use a high-accuracy gas sensor that cannot be used in a high-temperature environment.

According to the aspect of the present disclosure, the cooler may be arranged at least upstream of the gas sensor in the bypass pipe. As a result, the detection by the gas sensor can be performed in a state where the temperature of the exhaust gas is surely lowered.

According to the aspect of the present disclosure, the water stored in the water supply tank may be heated by combustion of gas fuel, and the cooler may cool the bypass pipe by using the water being supplied to the water supply tank. Since the water being supplied to the water supply tank is used as a refrigerant, the cooler can be provided at low cost.

According to the aspect of the present disclosure, a check valve may be arranged at a position in the main pipe between an inlet and an outlet of the bypass pipe. The pressure of the exhaust gas varies according to a combustion state of the gas fuel. However, when the pressure of the exhaust gas is low, the check valve in the main pipe is closed, and all the exhaust gas flows into the bypass pipe. When the pressure of the exhaust gas rises and the check valve opens, the exhaust gas flows through both the main pipe and the bypass pipe. Therefore, even when the pressure of the exhaust gas is low, the detection by the gas sensor can be reliably performed.

According to the aspect of the present disclosure, the check valve may be opened when a flow rate of the exhaust gas flowing through the bypass pipe exceeds a certain value. The check valve may be configured such that a pressure of the exhaust gas flowing through the main pipe is equal to a pressure of the exhaust gas flowing through the bypass pipe. According to this configuration, the flow rate of the exhaust gas flowing through the bypass pipe can be limited, and the cooling by the cooler can be performed effectively. Further, the load on the bypass pipe can be reduced.

Hereinafter, embodiments for implementing the present disclosure will be described referring to drawings. In each embodiment, portions corresponding to the elements described in the preceding embodiments are denoted by the same reference numerals, and redundant explanation may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. Not only a combination of parts that clearly indicate that the combination is possible in each embodiment, but also a partial combination of embodiments even if the combination is not specified is also possible when there is no problem in the combination.

First Embodiment

A first embodiment will be described with reference to FIGS. 1 to 6. FIG. 1 shows a configuration of a gas water heater 1 of the present embodiment, which is an example of a gas combustor. Water is supplied to an inside of a hot water supply tank 2 from a tap (not shown) via a water supply pipe 3. The hot water supply tank 2 includes therein a combustion pipe 4, and the water is heated to become hot water by combustion of gas inside the combustion pipe 4. The hot water is supplied to the outside through a discharge pipe 5. A temperature sensor (not shown) for detecting a temperature of the hot water is disposed in the discharge pipe 5.

An intake pipe 6 is connected to the hot water supply tank 2, and a blower 7 is arranged inside the intake pipe 6. The blower 7 is driven and controlled by a controller 8 positioned outside the intake pipe 6 and takes in atmospheric air from the outside. A gas supply pipe 9 is connected to an intermediate portion of the intake pipe 6 via a proportional valve 10. The proportional valve 10 is driven and controlled by the controller 8. As a result, an amount of gas supplied to the intake pipe 6 is adjusted.

Mixed gas which is a mixture of the gas inside the intake pipe 6 and the atmospheric air is supplied to the combustion pipe 4 via an injection unit 12. The mixed gas in the combustion pipe 4 is ignited by an igniter (not shown) and burned. The combustion pipe 4 is connected to the intake pipe 6 at the upper part of the hot water supply tank 2 in FIG. 1.The combustion pipe 4 includes a main portion 4 a that extends straight downward in the hot water supply tank 2, a return portion 4 b that is connected to a lower end of the main portion 4 a and extends upward from the lower part of the hot water supply tank 2, and a spiral portion 4 c that extends downward from an upper end of the return portion 4 b and spirally surrounds the circumference of the main portion 4 a. An exhaust pipe 13 is connected to the spiral portion 4 c, and the gas after combustion is discharged to the outside of the hot water supply tank 2.

As shown in FIG. 2, the exhaust pipe 13 includes a main pipe 14 and a bypass pipe 15. The bypass pipe 15 branches from the main pipe 14 such that the bypass pipe 15 allows exhaust gas to flow therethrough and then returns to the main pipe 14. The bypass pipe 15 is set to be smaller in cross-sectional area than the main pipe 14. As shown in FIG. 2, the bypass pipe 15 is a U-shaped pipe connected to a lower side of the main pipe 14, and the connection points to the main pipe 14 are an inlet 15 a and an outlet 15 b. A check valve 16 is arranged between the inlet 15 a and the outlet 15 b in the main pipe 14.

The bypass pipe 15 includes, for example, a gas sensor 17 of a constant potential electrolysis type that detects a gas concentration such as NOx in the exhaust gas. A cooler 18 as a cooler is arranged upstream of the gas sensor 17. Although not specifically shown, the cooler 18 may be a configuration that performs circulation of refrigerant. For example, the cooler 18 includes a refrigerant pipe wound around the outer periphery of the bypass pipe 15, and the refrigerant flows therethrough to cool the exhaust gas in the bypass pipe 15. The cooler 18 decreases the temperature of the refrigerant that has been increased by the exhaust gas flowing in the bypass pipe 15, and pumps the refrigerant to the refrigerant pipe.

The controller 8 includes, for example, a microcontroller that includes an input unit 21, a processing unit 22, and an output unit 23. The input unit 21 receives a sensor signal output from the gas sensor 17 or the temperature sensor and outputs the sensor signal to the processing unit 22. The processing unit 22 outputs a signal for controlling the blower 7 and the proportional valve 10 via the output unit 23 according to the input sensor signal. As a result, the controller 8 controls the amounts of air and gas fuel supplied to the combustion pipe 4, thereby controlling the combustion state of the gas water heater 1 and setting the temperature of hot water to the temperature set by a user.

Next, operations of the present embodiment will be described with reference to FIGS. 3 to 5. FIG. 3 shows a case where the gas water heater 1 is operated in a low thermal power mode and the pressure of the exhaust gas flowing through the exhaust pipe 13 is relatively low. Since the check valve 16 in the main pipe 14 is closed, the exhaust gas flows only through the bypass pipe 15.

On the other hand, FIG. 4 shows a case where the gas water heater 1 is operated in a high thermal power mode and the pressure of the exhaust gas flowing through the exhaust pipe 13 is relatively high. Since the check valve 16 is open, the exhaust gas flows through both the main pipe 14 and the bypass pipe 15. FIG. 5 is a time chart showing a case where the operating mode of the gas water heater 1 changes from the one shown in FIG. 3 to the other shown in FIG. 4. When the thermal power mode changes from “low” to “high”, the closed check valve 16 starts opening. At the same time, the flow rate of the exhaust gas in the main pipe 14 starts increasing from zero, and the flow rate of the exhaust gas in the bypass pipe 15 also increases. The flow rate of the bypass pipe 15 reaches an upper limit before the check valve 16 is fully opened, but the flow rate of the main pipe 14 becomes constant when the check valve 16 is fully opened.

A method of adjusting the pressures of the exhaust gas flowing through the main pipe 14 and the bypass pipe 15 so as to be the same when the check valve 16 is opened will be described with reference to FIG. 6. Each parameter is shown below.

A1: Diameter of the main pipe 14

A2: Diameter of the bypass pipe 15

v1: Maximum flow rate that can keep the check valve 16 closed

v2: Maximum flow rate that can be passed through the bypass pipe 15

v2=v1×A1/A2

Further, the pipe losses (1) to (3) shown in FIG. 6 are as follows.

Pipe loss (1): Loss due to bending of the flow path from the main pipe 14 to the bypass pipe 15 at right angle and changing in cross-sectional area

Pipe loss (2): Loss due to bending of the flow path in the bypass pipe 15 at right angle at two positions.

Pipe loss (3): Loss due to bending of the flow path from the bypass pipe 15 to the main pipe 14 at right angle and changing in cross-sectional area.

Although a loss occurs even in a portion where the flow path of the bypass pipe 15 is straight, it is ignored here because it is slight.

ΔP1 is the pipe loss (1) and expressed by the equation (1).

ΔP1=0.946×ρ·v1²/2+(1/Cc−1)×ρ·v2²/2   (1)

“ρ” is the density of water, and “Cc” is a constant determined by the pipe diameter ratio (A1/A2). ΔP2 is the pipe loss (2) and expressed by the equation (2).

ΔP2=0.946×ρ·v2²/2×2   (2)

ΔP3 is the pipe loss (3) and expressed by the equation (3).

ΔP3=(1−A2/A1)×ρ·v2²/2   (3)

Pressure loss P_(L) at the maximum flow rate v2 that can flow through the bypass pipe 15 is the sum of the above losses (1) to (3).

P _(L) =ΔP1+ΔP2+ΔP3   (4)

Therefore, since the check valve 16 employs a check valve in which a loss generated is equal to the pressure loss P_(L), the check valve 16 starts opening when the flow rate exceeds v2. As a result, the pressure of the exhaust gas flowing through the main pipe 14 becomes equal to the pressure of the exhaust gas flowing through the bypass pipe 15.

As described above, according to the present embodiment, in the gas water heater 1, the bypass pipe 15 is branched from the main pipe 14 of the discharge pipe 13 and is set so that the flow rate of the exhaust gas becomes smaller in the bypass pipe 15 than in the main pipe 14. The gas sensor 17 is arranged in the bypass pipe 15, and the bypass pipe 15 is cooled by the cooler 18. According to this configuration, the cooler 18 can be small and low cost because the cooler 18 is just required to cool the bypass pipe 15 having a relatively small flow rate of exhaust gas. Therefore, it is possible to use the high-accuracy gas sensor 17 that cannot be used in a high-temperature environment.

The cooler 18 may be arranged upstream of the gas sensor 17 in the bypass pipe 15. Accordingly, the gas sensor 17 can perform sensing in a state where the temperature of the exhaust gas is surely lowered.

Further, in the main pipe 14, a check valve 16 is arranged between the inlet 15 a and the outlet 15 b of the bypass pipe 15. When the pressure of the exhaust gas is low, the check valve 16 in the main pipe 14 is closed. Since all exhaust gas flows through the bypass pipe 15, the sensing by the gas sensor 18 can be reliably performed.

The check valve 16 is adjusted such that the check valve 16 is opened when the flow rate of the exhaust gas flowing through the bypass pipe 15 exceeds a certain value, and the pressures of the exhaust gas flowing through the main pipe 14 and the bypass pipe 15 become the same. According to this configuration, the flow rate of the exhaust gas flowing through the bypass pipe can be limited, and the cooling by the cooler can be performed effectively. Further, the load on the bypass pipe can be reduced.

Second Embodiment

Hereinafter, the same parts as those in the first embodiment are assigned the same reference numerals, and explanations thereof are omitted. Differences from the first embodiment will be described. As shown in FIGS. 7 and 8, the gas water heater 31 of the second embodiment includes a water supply pipe 32 instead of the water supply pipe 3. The water supply pipe 32 is arranged below the bypass pipe 15 along the bypass pipe 15. That is, in the second embodiment, the water supply pipe 32 is used as a cooler.

Water flowing through the water supply pipe 32 is used as a refrigerant, and heat is exchanged between the water supply pipe 32 and the bypass pipe 15. As a result, the bypass pipe 15 is cooled by the heat of the bypass pipe 15 being taken away by the water. The water supply pipe 32 may be arranged so as to be in contact with the bypass pipe 15. Alternatively, a heat dissipation sheet or the like may be interposed between the bypass pipe 15 and the water supply pipe 32 and perform heat exchange therebetween. As a result, the cooler can be provided at low cost.

The present disclosure is not limited only to the embodiments described above or shown in the drawings, and may be modified or expanded as follows.

The position of the cooler 18 may be changed as appropriate.

Not limited to the gas water heater, the present disclosure can be applied to another device as long as it utilizes the heat generated at combustion of gas.

While the present disclosure has been described with reference to various exemplary embodiments thereof, it is to be understood that the disclosure is not limited to the disclosed embodiments and constructions. To the contrary, the disclosure is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosure are shown in various combinations and configurations, which are exemplary, other various combinations and configurations, including more, less or only a single element, are also within the spirit of the disclosure. 

What is claimed is:
 1. A gas combustor comprising: a main pipe as an exhaust pipe that discharges exhaust gas generated at combustion of gas fuel; a bypass pipe that branches from the main pipe and is set to be smaller in flow rate of the exhaust gas than the main pipe; a gas sensor arranged in the bypass pipe to detect a gas contained in the exhaust gas; and a cooler that cools the bypass pipe.
 2. The gas combustor according to claim 1, wherein the cooler is arranged at least upstream of the gas sensor in the bypass pipe.
 3. The gas combustor according to claim 2, comprising a water supply tank to which water is supplied, wherein the water stored in the water supply tank is heated by the combustion of the gas fuel, and the cooler cools the bypass pipe by using the water being supplied to the water supply tank.
 4. The gas combustor according to claim 1, comprising a check valve provided at a position in the main pipe between an inlet and an outlet of the bypass pipe.
 5. The gas combustor according to claim 4, wherein the check valve is configured to be opened when a flow rate of the exhaust gas flowing through the bypass pipe exceeds a certain value, and the check valve is configured such that a pressure of the exhaust gas flowing through the main pipe becomes equal to a pressure of the exhaust gas flowing through the bypass pipe.
 6. The gas combustor according to claim 5, wherein the check valve is configured to generate a pressure loss of the exhaust gas flowing therethrough which is equal to a pressure loss in the bypass pipe at a maximum flow rate of the exhaust gas. 